Electrolytic cavity sinking apparatus



March 4, 1969 J BENDER ET AL Re. 26,531

ELECTROLYTIC CAVITY szmmm APPARATUS Original Filed June 21, 1960 UnitedStates Patent Oflice Re. 26,531 Reissued Mar. 4, 1969 26,531ELECTROLYTIC CAVITY SINKING APPARATUS Joseph L. Bender, Wheeling, andLynn A. Williams, Winnetka, Ill., assignors to Anocut EngineeringCompany, Elk Grove Village, Ill., a corporation of Illinois Original No.3,309,303, dated Mar. 14, 1967, Ser. No. 464,045, June 15, 1965, whichis a division of Ser. No. 37,766, June 21, 1960, now Patent No.3,214,360, dated Oct. 26, 1965. Application for reissue Aug. 14, 1967,Ser. No. 663,462 Matter enclosed in heavy brackets appears in theoriginal patent hut forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue. US. Cl.204224 15 Claims Int. Cl. B2311 1/00 ABSTRACT OF THE DISCLOSURE Anelectrolytic cavity sinking apparatus having a cathodic electrode, andmeans for pumping an electrolyte from a source through a work gapbetween the electrode and a workpiece under high pressure and at a highvelocgap. The bushing is driven against the entry face of the workpieceby an unbalanced force acting on it which is created by pressurizedelectrolyte.

This application is a division of copending application Ser. No. 37,766,filed June 21, 1960, entitled, Electrolytic Cavity Sinking Apparatus,now issued into Patent No. 3,214,360, dated Oct. 26, 1965.

The present invention relates generally to electrolytic cavity sinkingor shaping apparatus of the type disclosed in Lynn A. Williams PatentNo. 3,058,895, dated Oct. 16, 1962, for Electrolytic Shaping, and in thecopcnding application of Lynn A. Williams and James E. Davis, Scr. No.436,383, filed Dec. 23, 1964, for Control and Opcrating System forElectrolytic Hole Sinking.

The present invention is concerned with controlling the action of theelectrode and the electrolyte so as substantially to eliminate or reducetroublesome lateral vibration of electrodes used in both cavity sinkingand workpiece shaping operations, and to control the breakthrough of theelectrode at the remote side of the workpiece to produce a true hole oropening without irregularities and without excessive sparking betweenthe workpiece and the electrodc.

In general, apparatus of the type disclosed in the foregoing patent andapplication includes a fixture for securely mounting the workpiece, ahollow electrode having a working tip of electrically conductivematerial, a ram head mounting the electrode for movement toward theworkpiece, an electric power supply connected to the electrode and tothe workpiece so as to make the workpiece anodic and the electrodecathodic and capable of delivering a low voltage (5 to volts), highdensity (500 to 8000 amperes per square inch) direct current, and asource of electrolyte capable of delivering electrolyte at a highvelocity in the work gap between the electrode and the workpiece and ata pressure of about to 200 pounds per square inch.

It has been found from practical experience that one of the difliculticsin obtaining the maximum rate of penetration of the electrode into theworkpiece is that the electrode tends to vibrate laterally, therebycausing short-circuiting against one of the side surfaces, either on theinternal bore of the electrode or externally, or both. It now has beendiscovered that one of the things which causes or effects the lateralvibration is the tendency to store energy within the column of liquidinside the electrode. The cause of the oscillation which usually occursat a frequency within the sonic range appears to be the fact that theelectrolyte is being delivered in the work gap at an exceedingly highvelocity and under a very high pressure in the range, as previouslystated, of 150 to 200' pounds per square inch. When it is consideredthat the work gap between the electrode and the surface of the workpiecebeing acted upon is in the order of .002", it is not surprising thatthere is a feed-back oscillation in the column of liquid in theelectrodes passageway. It is a principal object of the present inventionto provide means associated with the electrode and the feed ofelectrolyte to dampen or break up this oscillation and thereby eliminatethe lateral vibration of the electrode within the hole being formed.

Another problem which has been encountered is in connection with throughbores or holes being formed in a workpiece. When the electrolyte is fedto the workpiece through the bore of the electrode, then as theelectrode approaches the remote or exit side of the workpiece, it willusually break through in some one area before it break through all theway around. This is due to the almost unavoidable irregularities in thesurface of the workpiece. When this occurs, the electrolyte then findsits way out through the broken-through opening at the exit side, insteadof turning back over the working tip of the electrode to return alongits axis to the entry surface of the workpiece. This is detected byobserving a jet of electrolyte squirting through an opening on the exitsurface of the workpiece. In Patent No. 3,058,895 arrangements aredisclosed to prevent this. One of them is to provide a dummy piecefastened to the exit surface of the workpiece by some adhesive such asWater glass. In another form, a backup material of soft rubber is used.It is obvious that these arrangements involve some inconvenience, and insome cases they are very difficult to use because the exit surface ofthe workpiece may lead into a more or less closed chamber which is notreadily accessible. Unless some form of backup device is used, andunless the electrode is advanced so that its working tip has passedcompletely through the workpiece and into the backup device, there willbe in the cavity adjacent the exit surfaces a sharp, inturned lip.

It is, therefore, an other primary object of the present invention toprovide a new arrangement for feeding the electrolyte and advancing theelectrode which will overcome the difficulties encountered in the breakthrough of the electrode from the exit side of the workpiece.

It should be noted that to a large extent the arrangement for overcomingthe lateral vibration also improves the exiting characteristics of theelectrode feed.

Another object is to provide new and improved electrolytic cavitysinking apparatus wherein the electrolyte is fed along the outer surfaceof the electrode to the work gap to exit through the bore of theelectrode.

Another object is to provide a new and improved electrolytic cavitysinking apparatus wherein the electrolyte is fed in such fashion thatany column of electrolyte Within the electrode is inhibited againstlongitudinal oscillation which will provide lateral vibration of theelectrode.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a schematic view of a portion of an electrolytic cavitysinking apparatus illustrating one form of the present invention;

FIG. 2 is a schematic view of an arrangement for backing up the cavityin the workpiece to assist in making clean through holes;

FIG. 3 is a view similar to FIG. 1 showing an electrode particularlyadapted for inhibiting longitudinal oscillations in the electrolytecolumn; and

FIG. 4 is a longitudinal sectional view through another form ofelectrode useful in inhibiting longitudinal oscillations of the columnof electrolyte.

In the drawings, there has been shown only so much of an electrolyticcavity sinking machine or apparatus as is necessary to an understandingof the present invention. Such apparatus is more completely disclosed inthe aforementioned Patent No. 3,058,895.

Referring now to FIG. 1, [the apparatus includes] an apparatus is shownin which a hollow, electrically conductive electrode is advanced towardand into an electrically conductive and electrochemically erodableworkpiece to establish a work gap for flow of high pressure electrolyteto support electrolytic current flow between said workpiece and saidelectrode.

The electrode 20 is mounted in an insulated bushing 28 which is slidablewith respect to the electrode. The bushing defines an endwise elongatedpassage (which in the embodiment shown has a cylindrical cross-section),and includes a transverse end wall structure defining a restricted endopening or bore 40 for said passage. The end wall structure presents arearwardly-facing surface 46 in the bushing 28, and an external surfaceor shoulder 42 surrounding the end opening and engageable in sealingrelation with the workpiece.

The electrode mounting means includes a piston-like electrode mount 26which is sealingly shiftable endwise in said ertdwise elongated,cylindrical passage, and is normally spaced from the end wall structureto define a chamber or annular operting 34 within said bushing meansbetween said mount and said end wall structure.

The mount carries the electrode as a transversely-reduced end extensionwhich projects through bore 40 in flow-clearance relation to define asecond, annular pussage extending between the chamber 34 and the workgap, the mount and electrode cooperatively defining a third passage orbore 48 extending between the work gap and a remote end region of themount. The chamber, the second passage, the work gap, and the thirdpassage define the electrolyte flow path which typically flows reverselythrough said electrode, from chamber 34 through said second passage,over the edge of working tip 22 and back through bore 48 in electrode20, the work gap being located intermediately in the flow path.

During electrolytic demetallization, the rearwardlyfacing surface 46 ofthe end wall structure of insulated bushing 28 is exposed to pressurizedelectrolyte in said flow path upstream of said gap, the pressure onsurface 46 urging the bushing 28 towards the workpiece.

FIG. 1 shows an electrode structure, indicated generally by thereference character 10, which is fastened by a flange 12 to a ram plate14. The ram plate is mounted on the forward end of a ram structure, andis insulated therefrom by an insulating block. The ram structureincludes a movable member powered from a positively driven screw (notshown) which will advance the electrode at a constant speed into anelectrically conductive and electrochemically erodable workpiece W. Themachine includes an electric power supply shown diagrammatically at 15,the output of which is connected by a cable or conductor 16 to the ramplate 14 and electrode 10, and a conductor 18 to the work through thetable and work holder which normally supports the workpiece W in place.

The power supply is capable of delivering, as previously mentionedherein, a low voltage (5 to volts), high density (500 to 8000 amperesper square inch) direct current in a sense to make the electrode 10negative and the workpiece W positive.

The electrode structure 10 includes the electrode proper at 20 having aworking tip 22 of slightly greater diameter than the shank or body ofthe electrode 20. The shank or body is coated, at least on its exteriorsurface, with an insulating material 24, which may be a vitreous enamelor an epoxy resin. If the electrode is of any substantial diameter, theinterior also will be provided with a coating of insulation similar tothe insulation 24.

The electrode 20 is made integral with or commonly mounted in anenlarged tubular, piston-like portion 26 which serves as the electrodemount, and which in turn is secured to the flange 12. Mounted on theelectrode mount 26 is a bushing 28 which may be made of a plasticmaterial impervious to chemical deterioration or damage by heat.Experimentally, an acrylic resin has been used and found to besatisfactory, but for a permanent insula tion a more durable material,such as Teflon resin, is preferred. The feed bushing 28 is mounted sothat it slides easily over the electrode mount 26 and has a clearancetherewith in the order of .002". To prevent excessive leakage ofelectrolyte a number of squared-bottomed, annular grooves 30 are cutinto the external surface of the electrode mount, and they provide asutficient seal to prevent excessive leakage of electrolyte between thefeed bushing 28 and the mount 26. The feed bushing is made in such a waythat at the inner end of its cylindrical bore 32 there is provided anannular opening 34 into which the electrolyte is fed under pressurethrough a supply line 36 and a fitting 38. The supply line 36 isconnected to a source of electrolyte under pressure which includes asupply tank or reservoir and a pump 37 capable of delivering electrolyteat a pressure of 150 to 200 pounds per square inch.

The bushing 28 is formed with a bore 40 at its exit end which is justlarge enough to permit being slipped over the working tip 22 of theelectrode 20 so that there is a clearance of several thousandths of aninch between the bore 40 of the bushing and the shank of the electrode20, thereby permitting the easy and adequate flow of electrolyte alongthe side wall of the electrode and down over the working tip 22. At itsexit end the guide bushing 28 is relieved to provide a sealing shoulder42 of reduced cross sectional area to permit sealing against the entrysurface of the workpiece W. Within the confines of the shoulder there isa recess 44 which is provided to accommodate the tip 22 of the electrodeto prevent its coming into contact with the entry surface of theworkpiece W when the initial erosion of the workpiece is being effected.

The feed bushing 28 is more or less permanently mounted on the electrodemount 26, and the entire assembly is then brought into close proximitywith the workpiece W with the bushing extended so that its sealingshoulder 42 touches the workpiece while the working tip 22 of theelectrode is slightly recessed within the bushing at 44. As electrolyteis fed through the flexible tube 36 and fitting 38 into the chamber 34,the elfect is to create a hydro. static force on the surface 46 of thechamber 34, thus urging the bushing into sealing engagement with theentry surface of the workpiece. Since the area of the frontal surface 46is substantially in excess of the effective area of the reduced sealingshoulder 42, the effect of any increase in work pressure from the ramstructure is increased sealing pressure, thereby completely eliminatingthe need for any mechanical clamp or the like.

The electrolyte finds its way along the exterior surface of theelectrode through the space in the bore 40 between the electrode and thesurface of the bore, over the edge of the working tip 22, and backthrough the bore 48 in the electrode 20. The exit path may be valvedthrough a needle valve and gauge if it is desired to observe and adjustthe back pressure. In the case of electrodes which are intended to beused many times in repetitive production operations, a simple exit holemay be provided in the electrode at its back end. In this case the borethrough the electrode mount is closed, as shown by the flange 12. If itis desired to adjust the back pressure, such may be done by an outletbushing, needle valve, and conduit leading to a drain. The drain, showndiagrammatically in FIG. 1, comprises a pan 49 in the bottom of the workarea and a conduit 51 leading to the reservoir 35. By arranging the exithole 50 so that it opens upwardly and is visible, it is possible to havean excellent visual indication of the rate of electrolyte flow. This canbe used for adjusting the in-feed rate of the electrode 20. The in-feedrate is increased up to the point where the reduction in the height ofthe fountain stream through the exit hole 50 indicates that the freeflow of electrolyte is being impeded by too close a gap between theworking tip 32 and the workpiece. This follows the teachings of PatentNo. 3,058,895 in that the fountain column of liquid constitutes a typeof flow meter, The amount of back pressure in the work gap is determinedby the size of the exit hole 50, and this usually will be adjusted sothat with an in-fed pressure in the order of 50 to 200 p.s.i., the backpressure at the exit hole 50 will range from approximately one foot headof electrolyte solution to a pressure of the order of a half, or evenmore than that, of the inlet pressure.

It will be appreciated that this arrangement maintains a solid column ofliquid all the way around the perimeter of the working tip 22. Inconsequence of this, the amount of side action is increased over thatwhich occurs when the electrolyte is applied to the bore of theelectrode. The result is to increase the overcut; that is, the excess ofthe size of the hole in the work with respect to the size of theelectrode working tip. Accordingly, either the electrode must beadvanced more rapidly, the supply voltage of direct current must belowered, the Width (in the direc tion of advance) of the working tipmust be narrowed, or some other means, such as an increase in allowancefor the amount of overcut, must be taken.

When the electrolyte is fed around the outside of the electrode, theproblem of breakthrough at the exit side is minimized, at least in thoseinstances where the plane of the working tip and the plane of the exitsurface are generally parallel. What happens is that, with the liquid,during the operation, passing completely around the outside of theelectrode and back through its bore with the electrode approaching theexit surface, a breakthrough may be achieved at one point prior toanother, but the liquid will continue to pass over the entire activearea of the working tip on its way to either of the exit paths; that is,the exit path through the bore 48 of the electrode, or through the newlycreated opening in the exit surface. In this way the electrode can beadvanced so that the working tip passes entirely through the workpiece,eliminating any inturned lip.

It has also been found that with this arrangement the electrode is lesssubject to lateral vibration or oscillation, as the solid column ofliquid surrounding it tends to dampen an oscillating tendency and toabsorb feedback energy sufficiently to prevent regeneration ofoscillatory impulses.

Where it is preferred to use a back-up member to improve thebreakthrough or exit condition, a preferred arrangement is shown in FIG.2, which illustrates only the workpiece W, a backup member 52, andassociated parts. The back-up member 52, which is made of a plasticsimilar to the plastic from which the bushing 28 is made, is shown asclamped in any suitable manner-for, example, by means of a C clamp 54tothe workpiece. A recess 56 is cut into the plastic back-up member at itsface which will be clamped against the exit face of the workpiece W, toa depth slightly greater than the thickness (in the direction ofadvance) of the working tip 22,

or whatever may be the normally uninsulated portion of the electrode 20.Extending away from the work and communicating with the recess 56 is asmall bleed hole 58. This arrangement functions substantially asfollows: As the electrode 20 breaks through the exit surface of theworkpiece W, there will be a slug of material, indicated by thereference character 60, which may have either a generally conical shape(as shown) if the electrode is not internally insulated, or it may havea substantially cylindrical shape if the interior of the electrode isinsulated (in this instance the words conical" and cylindrical are usedfor illustrative purposes only, because it is clear that the shapes willnot be a pure cone or cylinder if the shape of the electrode is otherthan round). As the breakthrough continues, it may be necessary ordesirable to prevent having the slug 60 hinge on the last remainingpoint of attachment to the workpiece W in such a way as to tip and causeshort-circuiting against the interior edge of the working tip or againstthe bore of the electrode if it be uninsulated. The depth of the recess56 is kept shallow enough to prevent this much cocking of the slug 60.The use of the bleed hole 58 assures that the pressure on the rear side62 of the slug is kept lower than that on the front side, so that thepressure differential urges the slug downwardly towards the bottom ofthe recess 56 without rattling or floating in an indeterminate manner inthe turbulent electrolyte. When the last point of attachment of the slug60 is eroded away, the slug moves under the pressure differential so asto close the bleed hole 58. Thus the slug moves out of the way so as topermit a. slight additional advance of the electrode 20 to clear awayany inturned lip at the exit surface of the work material.

A modified form of arrangement to overcome lateral vibration of theelectrode is shown in FIG. 3 wherein the electrode 20 is connected to aheader 64 carried on the ram plate 14. The flexible supply conduit 36from the pump is connected to the header 64 by the fitting 38. At thepoint where the liquid enters the electrode 20 from header 64, a plug90, having a relatively small hole 92 therethrough, is fitted into theelectrode so as to dampen oscillation in the column of electrolyte. Theelectrode 20 is shown insulated both on the inside and outside walls,and the diameter of the working tip in a typical installation is 5 Thebore of the tube is .333". The vibration dampening plug is inserted atthe inlet end of the electrode tube and it has a bore 92 A in diameter,and anywhere from to 1" in length. For smaller diameter electrodes,smaller damping restrictions will be used. It is believed that therestricted passage 92 introduces a resistive impedance to vibratory oroscillatory flow of the electrolyte. It is desired that the orifice 92be kept small to do this, but there still must be suycient electrolyteflow to prevent starving of the work gap through steaming and gasgeneration in the electrolyte. The restriction described with respect toa typical electrode is adequate to furnish enough electrolyte,particularly when the electrode 20 is fed with a close working gapagainst the work material. To prevent arcing and sparking a voltage inthe order of 7 to 8 volts is used with an electrolyte solutionconsisting of pounds of salts in 40 gallons of water. While therestrictive orifice 92 provides a sulficient amount of electrolyte, itdoes offer a restriction and friction, if there is any tendency of theliquid column to oscillate in the system at any troublesome frequency.Under these conditions the adsorption of oscillation in the narrowpassage is too great to permit sustaining the oscillation in the columnof electrolyte in the electrode.

In FIG. 4, there is shown another arrangement for preventing vibrationof the electrode. In this arrangement a very small hole 94 is formed inthe electrode immediately adjacent to its tip 22. After the electrode ismade and before it is insulated, a small hole 94, approximately .060",is drilled just behind the working tip. When the electrode is dipped inan epoxy type plastic of sufficient fluidity and low enough viscosity tocover the electrode with a thin film of insulation 24, in the order of.005"

in thickness, some of the material naturally is concentrated around andin the small hole near the tip. In some cases the hole may bepractically closed and remain so after the resin has been cured bybaking at about 350 F. The hole is then enlarged to a diameter ofapproximately .030" using a small drill usually held in a hand tool sothat care can be taken to prevent removing the insulating coating insuch a way as to expose any metal surface, which would cause shortcircuiting in the system. It is probable that the use of this hole,which may be called a weep hole, introduces a discontinuity ordissymetry in the system which breaks up the column of electrolyte inthe electrode 20, thereby preventing the existence of any sustainedoscillation.

While a number of expedients for effecting the objectives of the presentinvention have been shown, it is possible to generalize concerning themto the effect that all of them act upon the column of liquid in thecentral passage or passages of the electrode in such a way as to breakup any tendency of the column of the liquid to oscillate at a regularfrequency which is then translated into lateral vibrations. It is, ofcourse, possible to use various of these expedients in combination witheach other and with electrodes of different sizes and shapes, and it isexpected that this is what will be done. In an attempt to generalizeconcerning what has been done, it should be noted that the varioussystems shown include (1) introducing the electrolyte into the work gaparound the outer surface of the electrode, thereby cushioning the outersurface of the electrode and providing an easy means of regulating anyback pressure in the bore of the electrode by regulating the infeedrate; (2) introducing a resilience into the column of electrolyte in theoutlet from the system; (3) introducing an impedance into the liquidcolumn to retard the formation of oscillation; and (4) introducing adissyrnetry into the liquid flow pattern.

It is clear from the foregoing that the objectives which have beenclaimed for this invention at the outset of the specification have beenattained.

While preferred embodiments of the new and improved electrolytic cavitysinking apparatus constituting the present invention have been shown anddescribed, it will be apparent that numerous modifications andvariations thereof may be made without departing from the underlyingprinciples of the invention. It is therefore intended, by the followingclaims, to include all such variations and modifications by whichsubstantially the results of this invention may be obtained through theuse of substantially the same or equivalent means.

What is claimed as new and desired to be secured by United StatesLetters Patent is:

1. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and into an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cahthodic, andmeans for pumping an electrolyte from a source to the work gap betweenthe electrode and the workpiece under high pressure and at a highvelocity in the work gap, the combination therewith of an insulatedbushing surrounding the electrode and sealing against the entry face ofthe workpiece to form an electrolyte passage with the exterior of theelectrode, said bushing having a [cylindrical] bore therein, a tubularpiston-like mount connected to the electrode and slidable in said borein sealing relationship therewith, said tubular mount being connected tothe interior of the electrode to form an electrolyte outlet passage fromthe work gap, and means [connecting said electrolyte outlet passage tosaid electrolyte source] permitting exit of electrolyte from saidelectrolyte outlet passage.

2. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and into an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, and meansfor pumping an electrolyte from a source to the work gap between theelectrode and the workpiece under high pressure and at a high velocityin the work gap, the combination therewith of an insulated bushingsurrounding the electrode and sealing against the entry face of theworkpiece to form an electrolyte inlet passage with and around theexterior of the electrode, said bushing having a [cylindrical] boretherein, a tubular piston-like mount connected to the electrode andslidable in said bore in sealing relationship therewith, the interior ofsaid mount and the interior of the electrode being connected to eachother to provide an electrolyte outlet passage, and a restrictedelectrolyte outlet from said electrode mount communicating with saidoutlet passage to impose a back pressure on the electrolyte at the workgap[, and means connecting the outlet from said outlet passage to saidelectrolyte supply].

3. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and into an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, and meansfor pumping an electrolyte from a supply source to the work gap betweenthe electrode and the workpiece under high pressure and at high velocityin the work gap, the combination therewith of an insulated bushingclosely surrounding the electrode and having a surface sealing againstthe entry face of the workpiece in the area surrounding the electrode toform an inlet passage with and around the exterior of the electrode,said bushing having a [cylindrical] bore therein having a transversearea greater than that of said bushing surface sealing against the entryface of the workpiece, a tubular piston-like mount connected to theelectrode and slidable in said bore in sealing relationship therewith,the interior of said mount and the interior of the electrode beingconnected with each other to provide an electrolyte outlet passage, anda restricted electrolyte outlet in said electrode mount communicatingwith said outlet passage to impose a back pressure on the electrolyte atthe work gap[, and means connecting said outlet passage to saidelectrolyte supply].

4. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and into an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, and meansfor pumping an electrolyte from a supply source to the work gap betweenthe electrode and the workpiece under high pressure and at a highvelocity in the work gap, the combination therewith of an insulatedbushing having a passage therethrough with a transverse configurationcomplemental to that of the external shape of the electrode and closelysurrounding the electrode and from which the electrode projects, thespace between said bushing passage and the external surface of theelectrode forming an electrolyte inlet passage, said bushing having asurface surrounding the passage from which the electrode projects andsealing against the entry face of the workpiece, said bushing having a[cylindrical] bore therein in free communication with said inlet passageand having a transverse area greater than that of said bushing surfacesealing against the entry face of the workpiece, a tubular piston-likemount connected to the electrode slidable in said bore in sealingrelationship therewith and projecting from said bushing in a directionopposite to that of said electrode, the interior of said mount and theinterior of said electrode being connected to each other to provide anelectrolyte outlet passage, a restricted electrolyte outlet in saidelectrode mount where it has projected from said bushing andcommunicating with said outlet passage to impose a back pressure on theelectrolyte in the work gap, and means connecting said electrolyteoutlet passage to said electrolyte source.

5. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and into an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, and meansfor pumping an electrolyte through the electrode to the work gap betweenthe electrode and the workpiece under high pressure and at a highvelocity in the work gap, the combination therewith of a plug in theinlet end of the electrode having a single flow restricting passagetherethrough having a diameter about one-fifth that of the electrodetube, and having a length seven to sixteen times that of the passagediameter to damp the oscillations of the column of electrolyte withinthe hollow electrode.

6. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and into an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, and meansfor pumping an electrolyte through the electrode to the work gap betweenthe electrode and the workpiece under high pressure and at a highvelocity in the work gap, the improvement which comprises a bleed holein the side of the electrode against its tip communicating the interiorof the electrode to the atmosphere whereby the formation of oscillationsof the column of electrolyte within the hollow electrode is inhibitedthereby to prevent lateral vibration of the electrode.

7. In electrolytic cavity sinking apparatus having a hollow conductiveelectrode advanced toward and through an electrically conductive andelectrochemically erodable workpiece, means for passing a low voltage,high density direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, and meansfor pumping an electrolyte from a source to the work gap between theelectrode and the workpiece under high pressure and at a high velocityin the work gap, the combination therewith of means surrounding theelectrode and sealing against the entry face of the workpiece to form anelectrolyte passage between the exterior of the electrode and said lastnamed means, pressure operated means connected to said passage to urgesaid sealing means against the entry face of the workpiece, meansconnecting said electrolyte source to said passage, and a backup memberat the exit surface of the workpiece having a shallow cavity therein toreceive without appreciable cocking the slug of material from theworkpiece cavity, said backup member having a restrictive outlet passagefrom said cavity and opening to the atmosphere.

8. In electrolytic cavity sinking apparatus having a hollow electricallyconductive electrode advanced toward and into an electrically conductiveand electrochemically erodable workpiece to establish a work gap forflow of high pressure electrolyte to support electrolytic current fiowbetween said workpiece and said electrode, means for pumping anelectrolyte from a source to the work gap under high pressure and at ahigh velocity in the gap and for pumping said electrolyte from said gapto exit from the apparatus, and means for passing a low voltage, highdensity direct current between the workpiece and the electrode in asense to make the workpiece anodic and the electrode cathodic, thecombination therewith of electrode mounting means connected to saidpumping means for establishing an electrolyte flow path, said pathpassing through said electrode and having said work gap locatedintermediately therein, said electrode mounting means includinginsulated bushing means slidable with respect to said electrode, saidbushing means presenting a forwardly facing surface for sealing contactwith the workpiece at a region surrounding said gap, and also presentinga rearwardly facing surface responsive to pressure of electrolyte insaid path for urging said bushing means against the workpiece.

9. The apparatus of claim 8 wherein said rearwardly facing surface isexposed to electrolyte pressure at a path region upstream of said gap.

10. The apparatus of claim 8 wherein said path leads reversely throughsaid electrode and wherein said rearwardly facing surface is exposed toelectrolyte pressure at a path region upstream of said gap.

1]. The apparatus of claim 8 wherein said bushing means defines anendwise elongated passage and includes transverse end wall structuredefining a restricted end opening for said passage, said end wallstructure presenting said rearward/y facing surface at the workpiece endof said bushing means and an external surface surrounding said openingand engugeable in sealing relation with the workpiece, said electrodemounting means including a piston-like mount sealing/y shiftable endwisein said passage and normally spaced from said end wall structure todefine a chamber within said bushing means between said mount and saidend wall structure, said mount carrying said electrode as a transverselyreduced end extending through said chamber to project through saidopening in flow clearance relation to define a second passage extendingbetween the chamber and the work gap, said mount and said electrodecooperatively defining a third passage extending between the work gapand an exit hole at a remote end region of the mount, said chamber, saidsecond passage, said work gap and said third passage defining saidelectrolyte flow path.

12. In electrolytic cavity sinking apparatus having a hollowelectrically conductive electrode advanced toward and into anelectrically conductive and electrochemically erodable workpiece toestabish a work gap for flow of high pressure electrolyte to supportelectrolytic current flow between said workpiece and said electrode, theimprovement which comprises an insulated bushing means defining anendwise elongated passage and including an insulated transverse end wallstructure defining a restricted end opening for said passage, said endwall structure presenting an internal surface at the workpiece end ofsaid bushing means and an external surface surrounding said opening andengugeuble in sealing relation with the workpiece, a piston-like mountsealingly shiftable endwise in said passage and normally spaced fromsaid end wall structure to define a chamber within said bushing meansbetween said mount and said end wall structure, said mount carrying saidelectrode as a transversely reduced end extension extending through saidchamber to project through said opening in flow clearance relation todefine a second passage extending between the chamber and the work gap,said mount and said electrode cooperatively defining a third passageextending between the work gap and an exit hole at a remote end regionof the mount, said chamber, said second passage, said work gap and saidthird passage defining an electrolyte flow path, and means formaintaining a flow of high pressure electrolyte throng/1 said flow pathto establish an electrolyte pressure in said chamber acting on saidinternal surface to load said external surface against said workpiece insealing relation about said gap.

13. In electrolytic cavity sinking apparatus having a hollowelectrically conductive electrode adapted to be advanced toward and intoan electrically conductive and electrochemically erodable workpiece toestablish a work gap for flow of high pressure electrolyte to supportelectrolytic current flow between said workpiece and said electrode,means for pumping an electrolyte from a source to said work gap underhigh pressure and at a high velocity in the work gap and for pumpingsaid electrolyte from said gap to exit from the apparatus, and means forpassing a low voltage, high density direct current between the workpieceand the electrode in a sense to make the workpiece anodic and theelectrode cathodic, the combination therewith of electrode mountingmeans connected to said pumping means for establishing an electrolyteflow path passing through said electrode and having said work gaplocated intermediately therein, said electrode mounting means includingendwise shiftably mounted sleeve structure presenting a rearwardlyfacing surface responsive to pressure of electrolyte in said path forenabling electrolyte to urge said shiftably mounted sleeve structuretowards said workpiece.

14. The apparatus of claim 13 wherein said rearwardly facing surface isexposed to electrolyte pressure at a path region upstream of said gap.

15. The apparatus of claim 13 wherein said path leads reversely throughsaid electrode and wherein said rearwardly facing surface is exposed toelectrolyte pressure at a path region upstream of said gap.

References Cited The following references, cited by the Examiner, are

of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,308,860 1/1943 Clare 255-1 2,818,490 12/ 1957Dixon et a1 21969 2,909,641 10/1959 Kucyn 219-69 3,058,895 10/1962.Williams 204143 3,095,364 6/1963 Faust et a1. 204143 3,196,093 7/1965Williams 204143 3,219,568 11/1965 Wilkinson 204224 FOREIGN PATENTS335,003 7/ 1929 Great Britain. 1,130,245 5/ 1 962 Germany.

HOWARD S. WILLIAMS, Primary Examiner.

W. VAN SISE, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Reissue No. 26,531 March 4, 1969 Joseph L. Bender et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 33, "break" should read breaks line 55, "an other" shouldread another Column 4, between lines 51 and 52, insert electrode isfirst advanced toward the workpiece and the c l 5, li 51, "suycient"should read sufficient Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, J1. JR. Attesting Officer Commissioner of PatentsDedication Re. 26,531.J0seph L. Bender, \Vheeling, and Lynn A. Williams.\Vinnetka, Ill. ELECTROLYTIC CAVITY SINKING APPARATUS. Patent dated Mar.4, 1969. Dedication filed Dec. 23, 1971, by the ussignee, Anooutlingineem'ng Company.

Hereby dedicates t0 the Public the portion of the term of the patentsubsequent to Dec. 24, 1971.

[Oficial Gazette April 25, 197%]

